多线程同时下载文件即:在同一时间内通过多个线程对同一个请求地址发起多个请求,将需要下载的数据分割成多个部分,同时下载,每个线程只负责下载其中的一部分,最后将每一个线程下载的部分组装起来即可。
fileLength = conn.getContentLength();
//根据文件大小,先创建一个空文件
//“r“——以只读方式打开。调用结果对象的任何 write 方法都将导致抛出 IOException。
//“rw“——打开以便读取和写入。如果该文件尚不存在,则尝试创建该文件。
//“rws“—— 打开以便读取和写入,对于 “rw”,还要求对文件的内容或元数据的每个更新都同步写入到底层存储设备。
//“rwd“——打开以便读取和写入,对于 “rw”,还要求对文件内容的每个更新都同步写入到底层存储设备。
RandomAccessFile raf = new RandomAccessFile(filePath, "rwd");
raf.setLength(fileLength);
raf.close();
//计算各个线程下载的数据段
int blockLength = fileLength / threadCount;
分段完成后给每一个线程的请求头设置Range参数,他允许客户端只请求文件的一部分数据,每一个线程只请求下载相应范围内的数据,使用RandomAccessFile(可随机读写的文件)写入到同一个文件里即可组装成目标文件Range,是在 HTTP/1.1里新增的一个 header field,它允许客户端实际上只请求文档的一部分(范围可以相互重叠)
属性 | 解释 |
---|---|
bytes=0-499 | 表示头500个字节 |
bytes=500-999 | 表示第二个500字节 |
bytes=-500 | 表示最后500个字节 |
bytes=500- | 表示500字节以后的范围 |
bytes=0-0,-1 | 第一个和最后一个字节 |
HttpUrlConnection中设置请求头
URL url = new URL(loadUrl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
conn.setConnectTimeout(5000);
//若请求头加上Range这个参数,则返回状态码为206,而不是200
if (conn.getResponseCode() == 206) {
InputStream is = conn.getInputStream();
RandomAccessFile raf = new RandomAccessFile(filePath, "rwd");
raf.seek(startPosition);//跳到指定位置开始写数据
}
protected void onPause() {
if (mThreads != null)
stateDownload = DOWNLOAD_PAUSE;
}
protected void onStart() {
if (mThreads != null)
synchronized (DOWNLOAD_PAUSE) {
stateDownload = DOWNLOAD_ING;
DOWNLOAD_PAUSE.notifyAll();
}
}
synchronized (DOWNLOAD_PAUSE) {
if (stateDownload.equals(DOWNLOAD_PAUSE)) {
DOWNLOAD_PAUSE.wait();
}
}
取消下载即取消每个线程的执行,不建议直接使用Thread.stop()方法,安全的取消线程即run方法执行结束。只要控制住循环,就可以让run方法结束,也就是线程结束
while ((len = is.read(buffer)) != -1) {
//是否继续下载
if (!isGoOn)
break;
}
SharedPreferences sp = mContext.getSharedPreferences(SP_NAME, Context.MODE_PRIVATE);
//获取上次取消下载的进度,若没有则返回0
currLength = sp.getInt(CURR_LENGTH, 0);
for (int i = 0; i < threadCount; i++) {
//开始位置,获取上次取消下载的进度,默认返回i*blockLength,即第i个线程开始下载的位置
int startPosition = sp.getInt(SP_NAME + (i + 1), i * blockLength);
//结束位置,-1是为了防止上一个线程和下一个线程重复下载衔接处数据
int endPosition = (i + 1) * blockLength - 1;
//将最后一个线程结束位置扩大,防止文件下载不完全,大了不影响,小了文件失效
if ((i + 1) == threadCount)
endPosition = endPosition * 2;
mThreads[i] = new DownThread(i + 1, startPosition, endPosition);
mThreads[i].start();
}
网络获取和读写SD卡都需要添加相应权限
import android.content.Context;
import android.content.SharedPreferences;
import android.os.Handler;
import android.os.Message;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
/**
*
* 多线程下载文件
*/
public class DownLoadFile {
private static final String SP_NAME = "download_file";
private static final String CURR_LENGTH = "curr_length";
private static final int DEFAULT_THREAD_COUNT = 4;//默认下载线程数
//以下为线程状态
private static final String DOWNLOAD_INIT = "1";
private static final String DOWNLOAD_ING = "2";
private static final String DOWNLOAD_PAUSE = "3";
private Context mContext;
private String loadUrl;//网络获取的url
private String filePath;//下载到本地的path
private int threadCount = DEFAULT_THREAD_COUNT;//下载线程数
private int fileLength;//文件总大小
//使用volatile防止多线程不安全
private volatile int currLength;//当前总共下载的大小
private volatile int runningThreadCount;//正在运行的线程数
private Thread[] mThreads;
private String stateDownload = DOWNLOAD_INIT;//当前线程状态
private DownLoadListener mDownLoadListener;
public void setOnDownLoadListener(DownLoadListener mDownLoadListener) {
this.mDownLoadListener = mDownLoadListener;
}
interface DownLoadListener {
//返回当前下载进度的百分比
void getProgress(int progress);
void onComplete();
void onFailure();
}
public DownLoadFile(Context mContext, String loadUrl, String filePath) {
this(mContext, loadUrl, filePath, DEFAULT_THREAD_COUNT, null);
}
public DownLoadFile(Context mContext, String loadUrl, String filePath, DownLoadListener mDownLoadListener) {
this(mContext, loadUrl, filePath, DEFAULT_THREAD_COUNT, mDownLoadListener);
}
public DownLoadFile(Context mContext, String loadUrl, String filePath, int threadCount) {
this(mContext, loadUrl, filePath, threadCount, null);
}
public DownLoadFile(Context mContext, String loadUrl, String filePath, int threadCount, DownLoadListener mDownLoadListener) {
this.mContext = mContext;
this.loadUrl = loadUrl;
this.filePath = filePath;
this.threadCount = threadCount;
runningThreadCount = 0;
this.mDownLoadListener = mDownLoadListener;
}
/**
* 开始下载
*/
protected void downLoad() {
//在线程中运行,防止anr
new Thread(new Runnable() {
@Override
public void run() {
try {
//初始化数据
if (mThreads == null)
mThreads = new Thread[threadCount];
//建立连接请求
URL url = new URL(loadUrl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setConnectTimeout(5000);
conn.setRequestMethod("GET");
int code = conn.getResponseCode();//获取返回码
if (code == 200) {//请求成功,根据文件大小开始分多线程下载
fileLength = conn.getContentLength();
//根据文件大小,先创建一个空文件
//“r“——以只读方式打开。调用结果对象的任何 write 方法都将导致抛出 IOException。
//“rw“——打开以便读取和写入。如果该文件尚不存在,则尝试创建该文件。
//“rws“—— 打开以便读取和写入,对于 “rw”,还要求对文件的内容或元数据的每个更新都同步写入到底层存储设备。
//“rwd“——打开以便读取和写入,对于 “rw”,还要求对文件内容的每个更新都同步写入到底层存储设备。
RandomAccessFile raf = new RandomAccessFile(filePath, "rwd");
raf.setLength(fileLength);
raf.close();
//计算各个线程下载的数据段
int blockLength = fileLength / threadCount;
SharedPreferences sp = mContext.getSharedPreferences(SP_NAME, Context.MODE_PRIVATE);
//获取上次取消下载的进度,若没有则返回0
currLength = sp.getInt(CURR_LENGTH, 0);
for (int i = 0; i < threadCount; i++) {
//开始位置,获取上次取消下载的进度,默认返回i*blockLength,即第i个线程开始下载的位置
int startPosition = sp.getInt(SP_NAME + (i + 1), i * blockLength);
//结束位置,-1是为了防止上一个线程和下一个线程重复下载衔接处数据
int endPosition = (i + 1) * blockLength - 1;
//将最后一个线程结束位置扩大,防止文件下载不完全,大了不影响,小了文件失效
if ((i + 1) == threadCount)
endPosition = endPosition * 2;
mThreads[i] = new DownThread(i + 1, startPosition, endPosition);
mThreads[i].start();
}
} else {
handler.sendEmptyMessage(FAILURE);
}
} catch (Exception e) {
e.printStackTrace();
handler.sendEmptyMessage(FAILURE);
}
}
}).start();
}
/**
* 取消下载
*/
protected void cancel() {
if (mThreads != null) {
//若线程处于等待状态,则while循环处于阻塞状态,无法跳出循环,必须先唤醒线程,才能执行取消任务
if (stateDownload.equals(DOWNLOAD_PAUSE))
onStart();
for (Thread dt : mThreads) {
((DownThread) dt).cancel();
}
}
}
/**
* 暂停下载
*/
protected void onPause() {
if (mThreads != null)
stateDownload = DOWNLOAD_PAUSE;
}
/**
* 继续下载
*/
protected void onStart() {
if (mThreads != null)
synchronized (DOWNLOAD_PAUSE) {
stateDownload = DOWNLOAD_ING;
DOWNLOAD_PAUSE.notifyAll();
}
}
protected void onDestroy() {
if (mThreads != null)
mThreads = null;
}
private class DownThread extends Thread {
private boolean isGoOn = true;//是否继续下载
private int threadId;
private int startPosition;//开始下载点
private int endPosition;//结束下载点
private int currPosition;//当前线程的下载进度
private DownThread(int threadId, int startPosition, int endPosition) {
this.threadId = threadId;
this.startPosition = startPosition;
currPosition = startPosition;
this.endPosition = endPosition;
runningThreadCount++;
}
@Override
public void run() {
SharedPreferences sp = mContext.getSharedPreferences(SP_NAME, Context.MODE_PRIVATE);
try {
URL url = new URL(loadUrl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setRequestMethod("GET");
conn.setRequestProperty("Range", "bytes=" + startPosition + "-" + endPosition);
conn.setConnectTimeout(5000);
//若请求头加上Range这个参数,则返回状态码为206,而不是200
if (conn.getResponseCode() == 206) {
InputStream is = conn.getInputStream();
RandomAccessFile raf = new RandomAccessFile(filePath, "rwd");
raf.seek(startPosition);//跳到指定位置开始写数据
int len;
byte[] buffer = new byte[1024];
while ((len = is.read(buffer)) != -1) {
//是否继续下载
if (!isGoOn)
break;
//回调当前进度
if (mDownLoadListener != null) {
currLength += len;
int progress = (int) ((float) currLength / (float) fileLength * 100);
handler.sendEmptyMessage(progress);
}
raf.write(buffer, 0, len);
//写完后将当前指针后移,为取消下载时保存当前进度做准备
currPosition += len;
synchronized (DOWNLOAD_PAUSE) {
if (stateDownload.equals(DOWNLOAD_PAUSE)) {
DOWNLOAD_PAUSE.wait();
}
}
}
is.close();
raf.close();
//线程计数器-1
runningThreadCount--;
//若取消下载,则直接返回
if (!isGoOn) {
//此处采用SharedPreferences保存每个线程的当前进度,和三个线程的总下载进度
if (currPosition < endPosition) {
sp.edit().putInt(SP_NAME + threadId, currPosition).apply();
sp.edit().putInt(CURR_LENGTH, currLength).apply();
}
return;
}
if (runningThreadCount == 0) {
sp.edit().clear().apply();
handler.sendEmptyMessage(SUCCESS);
handler.sendEmptyMessage(100);
mThreads = null;
}
} else {
sp.edit().clear().apply();
handler.sendEmptyMessage(FAILURE);
}
} catch (Exception e) {
sp.edit().clear().apply();
e.printStackTrace();
handler.sendEmptyMessage(FAILURE);
}
}
public void cancel() {
isGoOn = false;
}
}
private final int SUCCESS = 0x00000101;
private final int FAILURE = 0x00000102;
private Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
if (mDownLoadListener != null) {
if (msg.what == SUCCESS) {
mDownLoadListener.onComplete();
} else if (msg.what == FAILURE) {
mDownLoadListener.onFailure();
} else {
mDownLoadListener.getProgress(msg.what);
}
}
}
};
}
import android.os.Bundle;
import android.os.Environment;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.TextView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
DownLoadFile downLoadFile;
private String loadUrl = "http://???????????.apk";
private String filePath = Environment.getExternalStorageDirectory()+"/"+"???.apk";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView tvprogress = (TextView) findViewById(R.id.tv_progress);
downLoadFile = new DownLoadFile(this,loadUrl, filePath, 3);
downLoadFile.setOnDownLoadListener(new DownLoadFile.DownLoadListener() {
@Override
public void getProgress(int progress) {
tvprogress.setText("当前进度 :"+progress+" %");
}
@Override
public void onComplete() {
Toast.makeText(MainActivity.this,"下载完成",Toast.LENGTH_SHORT).show();
}
@Override
public void onFailure() {
Toast.makeText(MainActivity.this,"下载失败",Toast.LENGTH_SHORT).show();
}
});
findViewById(R.id.bt).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
downLoadFile.downLoad();
}
});
findViewById(R.id.bt_pause).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
downLoadFile.onPause();
}
});
findViewById(R.id.bt_start).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
downLoadFile.onStart();
}
});
findViewById(R.id.bt_cancel).setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
downLoadFile.cancel();
}
});
}
@Override
protected void onDestroy() {
downLoadFile.onDestroy();
super.onDestroy();
}
}
关于多线程下载文件就说道这,若有不正之处,多多指教!